import java.util.Scanner;

public class d489 {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		String input, output;
		String[] sp_input;
		int a, b, c;
		int p; // 設p等於三角形三邊和的一半
		int s; // 海倫公式(已知三邊長的三角形面積) : s = Math.pow( ( p * ( p - a ) * ( p - b ) * ( p - c ) ) , 0.5 )
		
		while(sc.hasNext()) {
			input = sc.nextLine();
			sp_input = input.split(" ");
			
			a = Integer.parseInt(sp_input[0]);
			b = Integer.parseInt(sp_input[1]);
			c = Integer.parseInt(sp_input[2]);
			
			p = ( ( a + b + c ) / 2 );			
			s = ( p * ( p - a ) * ( p - b ) * ( p - c ) );
			output = Integer.toString(s);
			
			System.out.println(output);
		}
	}
	
}